1. Field of the Invention
The present invention relates to an optical filter for adding various functions such as antireflection, near-infrared shielding and electromagnetic wave shielding to various displays such as plasma display panel (PDP), cathode-ray-tube (CRT) display, liquid crystal display, organic EL (electroluminescence) display and field emission display (FED) including surface-conduction electron-emitter display (SED), and a display provided with the optical filter, particularly PDP.
2. Description of the Related Art
In flat-panel displays such as liquid crystal display, plasma display panel (PDP) and organic EL display, and CRT display, the problem that external light is reflected on a surface of the display to have difficult seeing visual information of the display has been known. Therefore, various countermeasures including provision of various optical films such as an antireflection film on the displays are taken.
In recent years, image magnification has entered the mainstream of the displays, and use of PDP and liquid crystal display have been generalized. PDP has advantages such as rapid response speed compared with the liquid crystal display. However, high-frequency pulse discharge is carried out in the light emitting part of the PDP for displaying image, and therefore unnecessary electromagnetic waves or infrared rays causing malfunction of infrared remote control are possibly radiated. Thus, as for the PDP, various antireflection films (electromagnetic wave shielding and light transmissive materials) having electric conductivity for PDP are proposed. Examples of the electromagnetic wave shielding light transmitting materials include (1) a transparent film having a metallic silver-containing transparent conductive thin layer thereon; (2) a transparent film having a conductive mesh layer consisting of network-patterned metallic wire or conductive fiber thereon; (3) a transparent film having network-patterned copper foil layer obtained by etching-processing copper foil so as to have opening parts thereon; (4) a transparent film having a mesh-shaped conductive ink layer formed by printing thereon.
However, the transparent conductive film (1) does not have sufficient high conductivity, and the conductive mesh (2) does not have generally sufficient high transparency. The etching-processing (3) and pattern printing (4) bring about formation of desired mesh-pattern conductive layer, and therefore have highly increased freedom in line width, line interval and pattern of the mesh compared with the conductive mesh (2). Hence, the etching-processing (3) and pattern printing (4) enable formation of a mesh-pattern conductive layer having high opening ratio such as 75% or more and fine line such as 200 μm or less. However, the etching-processing (3) requires expensive system (equipment) and involved process to bring about high production costs. On the other hand, the mesh-pattern printing (4) facilitates formation of the above-mentioned conductive layer, and therefore if a conductive layer having fine line and large mesh can be formed by mesh-pattern printing (4), the conductive layer has excellent light transmission and free from moire phenomenon. However, the pattern printing of conductive ink (4) requires high viscosity for maintaining good dispersion condition of conductive particles in an ink, and hence it is impossible to extremely reduce line width of ink and extremely increase opening ratio.
As the electromagnetic wave shielding light transmissive material, for example, patent document 1 (JP11-074683-A) describes an electromagnetic wave shielding light transmissive material obtained by placing the conductive mesh (mesh-shaped metal foil) (3) between two transparent plates and bonding them by transparent adhesive resin to unit them. The adhesive is thermoplastic resin such as ethylene/vinyl acetate copolymer (EVA).
In order to extremely enhance the opening ratio, patent document 2 (JP2001-332889-A) discloses a process for forming a mesh-shaped conductive layer wherein the mesh-pattern printing (4) is improved. The process is capable of preparing an electromagnetic wave shielding light transmissive material having sufficiently reduced line width of ink and extremely increased opening ratio, and the process comprises forming dots on a surface of a film by using conductive material soluble in water, forming a conductive material layer comprising conductive material insoluble in water on the surface of the film, and bringing water in contact with the surface of the film to remove the dots and the conductive material layer on the dots (hereinafter referred to as “printing mesh process”).
Patent document 1: JP 11-074683-A
Patent document 2: JP2001-332889-A